This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Diagnostic and Statistical Manual of Mental Disorders (4th Edition) (DSM IV-TR 2000) classifies BPD as an Axis II Cluster B Personality Disorder. DSM IV criteria for BPD include affective instability, impulsive risk taking behavior, inappropriate and intense anger, unstable relationships that rapidly shift between idealization and devaluation, unstable self image, feelings of emptiness, dissociative experiences, self injurious behavior such as superficial skin cutting or burning, and multiple suicide attempts (DSM IV-TR 2000). The designation of BPD as an Axis II personality disorder reflects the historical conceptualization that personality disorders are psychologically and developmentally rooted, rather than biologically based and genetically determined such as the Axis I disorders. More recently, alternative conceptualizations of BPD and personality disorders have arisen, lending theoretical rationale for the use of medications in the treatment of BPD. The current study aims to assess the efficacy and tolerability of ziprasidone in the treatment of borderline personality disorder. The overall aim of this study is to determine the efficacy of ziprasidone in the treatment of BPD via a 10-week placebo-controlled trial in 40 adult participants. Ziprasidone is currently approved for the treatment of manic and mixed episodes by the U.S. Food and Drug Administration. HYPOTHESIS: PRIMARY HYPOTHESIS: 1. Ziprasidone will be superior to placebo in treating global severity, as measured by the ZAN-BPD. SECONDARY HYPOTHESIS: 1. Ziprasidone will be superior to placebo in treating global severity as measured by the CGI-I. 2. Ziprasidone will be superior to placebo in improving manic-spectrum symptoms, as measured by the Young Mania Rating Scale. 3. Ziprasidone will be superior to placebo in treating irritability and aggression, as measured by the Overt Aggression Scale - Modified. 4. Ziprasidone will be superior to placebo in treating affective instability as measured by the Affective Lability Scale (ALS). 5. Ziprasidone will be superior to placebo in improving functional disability, as measured by the Sheehan Disability Scale.